Process of making polyester latex with buffer

ABSTRACT

Methods herein include mixing at least one polyester resin with at least one solvent to form a resin mixture, adding water to cause phase inversion and form a polyester latex, adding at least one buffering agent to the phase inverted mixture to stabilize the phase inverted mixture, and subsequent to the buffering agent addition, substantially removing the at least one solvent from the phase inverted mixture.

TECHNICAL FIELD

The present disclosure relates to a polyester latex and process formaking the same, wherein the formulation exhibits improved stabilitywith narrow particle size distribution and less latex sedimentation. Thepolyester latexes may be used to form toners in emulsion aggregationprocesses.

BACKGROUND

Emulsion aggregation (EA) is one of the many processes used for thepreparation of toners. Emulsion aggregation toners may be used informing print and/or xerographic images. Emulsion aggregation techniquesmay first involve the formation of a latex of the resin particles byheating the resin using a batch or semi-continuous emulsionpolymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943,the disclosure of which is hereby incorporated by reference in itsentirety. Other examples of emulsion/aggregation/coalescing processesfor the preparation of toners are illustrated in U.S. Pat. Nos.5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488; 5,977,210;5,994,020; and 7,858,285, the disclosures of each of which are herebyincorporated by reference in their entirety.

Polyester EA ultra low melt (ULM) toners have been prepared utilizingamorphous and crystalline polyester resins as illustrated, for example,in U.S. Pat. No. 7,547,499, the disclosure of which is herebyincorporated by reference in its entirety. The EA process requirespolyesters to be first formulated into latex emulsions, for example, bysolvent containing batch processes, such as solvent flash emulsificationand/or solvent-based phase inversion emulsification (PIE).

In PIE, polyester resins are typically converted into a latex bydissolving the polyester resin in at least one organic solvent, whichthen needs to be removed, sometimes referred to as skipped, via a vacuumdistillation process for safety and environmental concerns. However, dueto stability issues during the PIE process and during transportation andstorage, product loss can occur. For example, a polyester latex may gelinside the reactor and thus not form, or may form but settle out duringtransportation and storage. Accordingly, what is desired is an improvedPIE process for latex production in which the polyester latex isreliably produced and in which the resulting latex has good stability.

SUMMARY

The above and other objects are achieved herein, wherein in embodiments,the present disclosure describes a process comprising mixing at leastone polyester resin with at least one solvent to form a resin mixture,adding water to cause phase inversion and form a polyester latex, addingat least one buffering agent to the phase inverted mixture to stabilizethe phase inverted mixture, and subsequently substantially removing theat least one solvent from the phase inverted mixture.

In another aspect of the present disclosure, a process comprises mixingat least one polyester resin with at least one solvent to form amixture, phase inverting the mixture by adding water, buffering thephase inverted mixture, preventing foaming of the buffered phaseinverted mixture by using a defoaming agent, and following phaseinverting, substantially removing the at least one solvent from thephase inverted mixture.

A crystalline polyester latex is also described in which the latex has ashelf-life stability of at least 3 months, and contains less than 600ppm of solvent, which is prepared by a process including mixing at leastone polyester resin with at least one solvent to form a mixture, phaseinverting the mixture using water, stabilizing the phase invertedmixture with a buffering agent; and subsequent to the buffering agentaddition substantially removing the at least one solvent from the phaseinverted mixture.

EMBODIMENTS

The processes herein include using a buffer, sometimes also referred toherein as buffering agent, for a more effective process of makingpolyester latexes via solvent-based phase inversion emulsification ofpolyesters. These polyester latexes, in turn, may be utilized for thepreparation of low melt polyester toners, for example, in an EA process.The present disclosure provides processes for forming a polyester latexwith significantly reduced and/or no gelling and sedimentation, and thusless product loss and significantly improved stability, compared tocurrent phase inversion processes in which no buffering agent isincluded.

In embodiments, the process includes mixing at least one polyester resinwith at least one solvent to form a resin mixture, adding water to causephase inversion and form a polyester latex, adding at least onebuffering agent to the phase inverted mixture to stabilize the phaseinverted mixture, and subsequent to the addition of the buffering agent,substantially removing the at least one solvent from the phase invertedmixture.

The processes herein are able to achieve a poly ester latex that has ashelf-life stability of at least 3 months. This polyester latex hasremarkably improved stability with much less solvent compared topolyester latexes prepared in a similar process but lacking addition ofany buffering agents following phase inversion. Without the addition ofa buffering agent, it was found that the crystalline polyester latex maybecome unstable at the late stage of distillation during the phaseinversion emulsification process. For example, the latex may become agel inside the reactor once the residual level of solvents falls below600 ppm. This results in a whole batch loss and a lot of effort neededto clean up the reactor. In other cases, the latex survives thedistillation stage, but latex gelation may still occur during storage.

Shelf-life stability can be assessed through the amount of sediment ofgelation of the latex during storage under conditions of roomtemperature and pressure. A typical centrifugation method can be used tosimulate storage and accelerate the sediment settling process. In theprocedure, two weeks of storage was simulated via an IEC Centrifuge at3,120 G-force for 50 seconds. The samples were removed and the amount ofsediment was then determined. The latex was considered stable if theamount of measured sediment of latex after centrifugation is less than 1weight percent of the total latex weight.

Any polyester resin may be utilized in making the polyester latexes inthe present disclosure. The resin may be an amorphous resin, acrystalline resin, and/or a combination thereof. The resin may be apolyester resin, such as described in U.S. Pat. Nos. 6,593,049 and6,756,176, the disclosures of each of which are hereby incorporated byreference in their entirety. Suitable resins may also include a mixtureof an amorphous polyester resin and a crystalline polyester resin asdescribed in U.S. Pat. No. 6,830,860, the disclosure of which is herebyincorporated by reference in its entirety.

One, two, or more polyester resins may be used. Where two or more resinsare used, the resins may be in any suitable ratio (e.g., weight ratio)such as, for example of from about 1% (first resin):99% (second resin)to about 99% (first resin):1% (second resin), in embodiments from about10% (first resin):90% (second resin) to about 90% (first resin):10%(second resin). Where the polyester resin includes an amorphouspolyester resin and a crystalline polyester resin, the weight ratio ofthe two resins may be from about 99% (amorphous polyester resin): 1%(crystalline polyester resin), to about 1% (amorphous polyester resin):99% (crystalline polyester resin).

The polyester resin may possess acid groups which, for example, may bepresent at the terminal of the resin. Acid groups which may be presentinclude carboxylic acid groups and the like.

In embodiments, the resin may be a polyester resin having an acid valuefrom about 2 mg KOH/g of resin to about 200 mg KOH/g of resin, or fromabout 5 mg KOH/g of resin to about 30 mg KOH/g of resin. The acid numbermay be detected by titration with KOH/methanol solution containingphenolphthalein as the indicator. The acid number may then be calculatedbased on the equivalent amount of KOH/methanol required to neutralizeall the acid groups on the resin identified as the end point of thetitration.

The polyester resin may be a polyester resin formed by reacting a diolwith a diacid or diester in the presence of an optional catalyst. Forforming a crystalline polyester, suitable organic diols includealiphatic diols with from about 2 to about 36 carbon atoms, such as1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,2,2-dimethylpropane-1,3-diol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol andthe like including their structural isomers. Examples of diols which maybe utilized in generating an amorphous polyester include1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, pentanediol, hexanediol, 2,2-dimethylpropanediol,2,2,3-trimethylhexanediol, heptanediol, dodecanediol,bis(hydroxyethyl)-bisphenol A, bis(2-hydroxypropyl)-bisphenol A,1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, xylenedimethanol,cyclohexanediol, diethylene glycol, bis(2-hydroxyethyl) oxide,dipropylene glycol, dibutylene, and combinations thereof. The aliphaticdiol may be, for example, used in an amount of from about 40 to about 60mole percent, from about 42 to about 55 mole percent, or from about 45to about 53 mole percent, and a second diol can be selected in an amountof from about 0 to about 10 mole percent, or from about 1 to about 4mole percent of the resin.

Examples of organic diacids or diesters including vinyl diacids or vinyldiesters selected for the preparation of crystalline polyester resinsinclude oxalic acid, succinic acid, glutaric acid, adipic acid, subericacid, azelaic acid, sebacic acid, fumaric acid, dimethyl fumarate,dimethyl itaconate, cis, 1,4-diacetoxy-2-butene, diethyl fumarate,diethyl maleate, phthalic acid, isophthalic acid, terephthalic acid,naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid,cyclohexane dicarboxylic acid, malonic acid and mesaconic acid, adiester or anhydride thereof. Examples of diacids or diesters includingvinyl diacids or vinyl diesters utilized for the preparation ofamorphous polyesters include dicarboxylic acids or diesters such asterephthalic acid, phthalic acid, isophthalic acid, fumaric acid,trimellitic acid, dimethyl fumarate, dimethyl itaconate, cis,1,4-diacetoxy-2-butene, diethyl fumarate, diethyl maleate, maleic acid,succinic acid, itaconic acid, succinic acid, succinic anhydride,dodecylsuccinic acid, dodecylsuccinic anhydride, glutaric acid, glutaricanhydride, adipic acid, pimelic acid, suberic acid, azelaic acid,dodecanediacid, dimethyl terephthalate, diethyl terephthalate,dimethylisophthalate, diethylisophthalate, dimethylphthalate, phthalicanhydride, diethylphthalate, dimethylsuccinate, dimethylfumarate,dimethylmaleate, dimethylglutarate, dimethyladipate, dimethyldodecylsuccinate, and combinations thereof. The organic diacid may beused in an amount of, for example, from about 40 to about 60 molepercent, from about 42 to about 52 mole percent, or from about 45 toabout 50 mole percent, and a second diacid can be selected in an amountof from about 0 to about 10 mole percent of the resin.

Specific examples of suitable crystalline polyester resins include, forexample poly(ethylene-adipate), poly(propylene-adipate),poly(butylene-adipate), poly(pentylene-adipate), poly(hexylene-adipate),poly(octylene-adipate), poly(ethylene-succinate),poly(propylene-succinate), poly(butylene-succinate),poly(pentylene-succinate), poly(hexylene-succinate),poly(octylene-succinate), poly(ethylene-sebacate),poly(propylene-sebacate), poly(butylene-sebacate),poly(pentylene-sebacate), poly(hexylene-sebacate),poly(octylene-sebacate), poly(decylene-sebacate),poly(decylene-decanoate), poly(ethylene-decanoate), poly(ethylenedodecanoate), poly(nonylene-sebacate), poly(nonylene-decanoate),copoly(ethylene-fumarate)-copoly(ethylene-sebacate),copoly(ethylene-fumarate)-copoly(ethylene-decanoate),copoly(ethylene-fumarate)-copoly(ethylene-dodecanoate),copoly(2,2-dimethylpropane-1,3-diol-decanoate)-copoly(nonylene-decanoate),poly(octylene-adipate). Suitable crystalline polyester resins which maybe utilized, optionally in combination with an amorphous polyester resinas described below, include those disclosed in U.S. Pat. No. 7,329,476,the disclosure of which is hereby incorporated by reference in itsentirety. A suitable crystalline polyester resin may include a resinformed of, for example, ethylene glycol and a mixture of dodecanedioicacid, and fumaric acid co-monomers. For example, a poly(propoxylatedbisphenol A co-fumarate) resin may be combined with a crystalline resin,for example poly(dodecandioicacid-co-nonanediol), to form a latexemulsion.

The crystalline resin may be present, for example, in an amount of fromabout 5 to about 50 percent by weight of the polyester resin mixture,such as from about 10 to about 35 percent by weight of the resinmixture. The crystalline resin can possess various melting points of,for example, from about 30° C. to about 120° C., or, from about 60° C.to about 90° C. The crystalline resin may have an average molecularweight (Mw), as measured by gel permeation chromatography (GPC) usingpolystyrene standards of, for example, from about 5,000 to about 90,000.

An unsaturated amorphous polyester resin may be utilized as a latexresin. Examples of such resins include those disclosed in U.S. Pat. No.6,063,827, the disclosure of which is hereby incorporated by referencein its entirety. Exemplary unsaturated amorphous polyester resinsinclude, for example, poly(propoxylated bisphenol co-fumarate),poly(ethoxylated bisphenol co-fumarate), poly(butyloxylated bisphenolco-fumarate), poly(co-propoxylated bisphenol co-ethoxylated bisphenolco-fumarate), poly(1,2-propylene fumarate), poly(propoxylated bisphenolco-maleate), poly(ethoxylated bisphenol co-maleate), poly(butyloxylatedbisphenol co-maleate), poly(co-propoxylated bisphenol co-ethoxylatedbisphenol co-maleate), poly(1,2-propylene maleate), poly(propoxylatedbisphenol co-itaconate), poly(ethoxylated bisphenol co-itaconate),poly(butyloxylated bisphenol co-itaconate), poly(co-propoxylatedbisphenol co-ethoxylated bisphenol co-itaconate), poly(1,2-propyleneitaconate), and combinations thereof. An example of a linearpropoxylated bisphenol A fumarate resin which may be utilized isavailable under the trade name SPAR11 from Resana S/A IndustriasQuimicas, Sao Paulo Brazil. Other propoxylated bisphenol A fumarateresins that may be utilized and are commercially available include GTUFand FPESL-2 from Kao Corporation, Japan, and EM181635 from Reichhold,Research Triangle Park, N.C.

The amorphous resin may be present, for example, in an amount of fromabout 30 to about 90 percent by weight of the formulation, or from about40 to about 80 percent by weight of the formulation. The amorphous resinor combination of amorphous resins utilized in the latex may have aglass transition temperature of from about 30° C. to about 80° C., suchas from about 35° C. to about 70° C. The resin(s) utilized in the latexmay have a melt viscosity of from about 10 to about 1,000,000 Pa*S atabout 130° C., such as, from about 50 to about 100,000 Pa*S.

In the processes herein, the polyester resin is mixed with an organicsolvent or solvent mixture to produce a homogenous resin mixture. Theresin mixture may be agitated and/or heated in order to decrease thetime necessary to produce a homogenous resin mixture. For example, theresin may be heated to a temperature necessary to dissolve or speed thedissolution of the resin in the solvent, for example, from about 30° C.to about 120° C., or form about 60° C. to about 90° C.

The present process includes mixing at least one polyester resin, whichmay be at an elevated temperature, with at least one organic solvent.The polyester resin may be an amorphous resin and an elevatedtemperature for mixing may be a temperature above the glass transitiontemperature of the polyester resin. In other embodiments, the polyesterresin may be a crystalline polyester resin and the elevated temperaturefor mixing may be a temperature above the melting point of the polyesterresin. In further embodiments, the polyester resin may be a mixture ofamorphous and crystalline polyester resins and the temperature formixing may be above the glass transition temperature of the mixture.

Any suitable organic solvent may be used to dissolve the resin and formthe mixture. For example, polyols of the formula C_(n)H₂₊₁OH, ketones ofthe formula C₂(H_(2n+2))CO, acetates of the formula C_(n)H_(2n+2)COCH₃,where n is greater than or equal to 1, esters, ethers, amines, andcombinations thereof may be used. Suitable organic solvents include, forexample, methanol, ethanol, propanol, isopropanol, butanol, ethylacetate, methyl ethyl ketone, tetrahydrofuran and the like, andcombinations thereof. In embodiments, the organic solvent may beimmiscible in water and may have a boiling point of from about 30° C. toabout 120° C. The solvent may be used in an amount of, for example, fromabout 1 wt % to about 100 wt % of the resin, from about 10% wt to about90% wt of the resin, or from about 25% wt to about 85% wt of the resin,where the solvent to resin ratio ranges from about 0.3 to about 3, orfrom about 0.5 to about 1.5.

After mixing the polyester resin with the solvent, but before phaseinversion, the resin mixture may optionally be mixed with a base orneutralizing agent, optionally at an elevated temperature. Theneutralizing agent may, for example, be a solid or added in the form ofan aqueous solution.

The neutralizing agent may be used to neutralize a base or an acid, forexample, the acid groups of the polyester resins, so a neutralizingagent herein may also be referred to as a “basic neutralization agent.”Any suitable basic neutralization agent may be used in accordance withthe present disclosure. For example, suitable basic neutralizationagents may include both inorganic basic agents and organic basic agents.Suitable basic agents may include ammonium hydroxide, potassiumhydroxide, sodium hydroxide, sodium carbonate, sodium bicarbonate,lithium hydroxide, potassium carbonate, organoamines such as triethylamine, and combinations thereof.

The neutralizing agent may be utilized so that it is present in anamount of from about 0.001% by weight to 50% by weight of the resin,from about 0.01% by weight to about 25% by weight of the resin, or fromabout 0.1% by weight to 5% by weight of the resin.

The neutralizing agent may be added at once in bulk, added in stages, ormetered, for example at a rate of from about 0.01% wt % to about 10 wt %about every 10 minutes, from about 0.5 wt % to about 5 wt % about every10 minutes, or from about 1 wt % to about 4 wt % about every 10 minutes.The rate of addition of the neutralizing agent need not be constant, andcan be varied.

The neutralizing agent may, for example, be added in the form of anaqueous solution. In addition, prior to addition, the neutralizing agentmay be at any suitable temperature, including room temperature (about20° C. to about 25° C.), or an elevated temperature, for example fromabout 30° C. to about 120° C., or form about 60° C. to about 90° C.

Utilizing the above basic neutralization agent in combination with apolyester resin possessing acid groups, a neutralization ratio of fromabout 50% to about 300% may be achieved, from about 70% to about 200%,or from about 100% to about 120%. The neutralization ratio may becalculated, for example, by using the following equation:Neutralization ratio in an equivalent amount of 10% NH₃/(resin (g)*resinacid value*0.303*0.01).

The addition of the basic neutralization agent may thus raise the pH ofthe mixture including a resin possessing acid groups to be about 5 toabout 14, such as to a pH of about 6 to about 11. The addition of theneutralizing agent may be useful, for example, where the polyester resinutilized possesses acid groups. The neutralizing agent may neutralizethe acidic groups of the resin, thereby enhancing the subsequentformation of the phase-inverted emulsion and formation of particlessuitable for use in forming toner compositions.

For the phase inversion process, the amorphous and/or crystallinepolyester resin is desirably dissolved in a low boiling organic solvent,which solvent is immiscible in water, such as ethyl acetate, or methylethyl ketone, or any other suitable solvent, at a concentration of, forexample, from about 1 wt % to about 75 wt % of resin in solvent, or fromabout 5 wt % to about 60 wt %. The resin mixture may be heated to atemperature of, for example, about 25° C. to about 90° C., or from about30° C. to about 85° C. The heating need not be held at a constanttemperature, but may be varied. For example, the heating may be slowlyor incrementally increased during heating until a desired temperature isachieved.

While the temperature is maintained in the aforementioned range, wateris added to the mixture to cause phase inversion. The water may be addedin any form, for example as deionized water, as an aqueous solution, forexample as an aqueous solution with the neutralization agent, or anyother aqueous solution. The addition of a sufficient amount of waterforms a phase inverted latex. The water to resin weight ratio is, fromabout 1 to 80, or from about 5 to about 50. The water is desirablymetered into the resin mixture, for example added to the mixture at arate of about 0.1% to about 10% of resin weight of water per minute, orfrom about 0.5% to about 4% of resin weight per minute. The water may bewarmed before addition to the resin mixture to a temperature from about25° C. to about 80° C., or from about 30° C. to about 70° C.

The water may be added as part of an aqueous solution until phaseinversion occurs, or a portion of the water may be added as part of anaqueous solution followed by a separate addition of additional water tocause phase inversion. The total amount of water added to the resinmixture is for example, from about 1 wt % to about 25 wt % of the resin,such as from about 5 wt % to about 20 wt %.

In an example embodiment, an aqueous solution of the neutralizationagent, and an optional surfactant, may be metered into a heated resinmixture at least until phase inversion is achieved, or theneutralization agent and optional surfactant may be metered into theheated mixture to neutralize the solution followed by an addition of awater, for example, deionized water, until phase inversion is achieved.

Where the process further includes adding water after the addition of,for example, a basic neutralization agent and optional surfactant, thewater may be metered into the mixture at a rate of, for example, about0.01 wt % to about 10 wt % about every minute, from about 0.5 wt % toabout 5 wt % about every minute, or from about 1 wt % to about 4 wt %every 10 minutes. The rate of water addition need not be constant, andcan be varied.

In embodiments, a process of the present disclosure may include heatingone or more ingredients of a polyester resin composition to an elevatedtemperature, stirring the resin composition, and, while maintaining thetemperature at the elevated temperature, optionally adding theneutralizing agent, and optional surfactant into the mixture to enhanceformation of the emulsion including a disperse phase and a continuousphase including the resin composition, and continuing to add theneutralizing agent, optional surfactant and/or water until phaseinversion occurs to form the phase inverted emulsion.

Although the point of phase inversion may vary depending on thecomponents of the emulsion, the temperature of heating, the stirringspeed, and the like, phase inversion may occur when water has been addedso that the resulting resin is present in an amount from about 5 wt % toabout 70 wt % by weight of the emulsion, from about 20 wt % to about 65wt % by weight of the emulsion, or from about 30 wt % to about 60 wt %by weight of the emulsion.

At phase inversion, polyester resin particles become emulsified anddispersed within the aqueous phase. That is, an oil-in-water emulsion ofthe polyester resin particles in the aqueous phase is formed. Phaseinversion may be confirmed by, for example, measuring via any of thetechniques within the art.

Stirring may be utilized to enhance formation of the phase invertedemulsion. Any suitable stirring device may be utilized. The stirringneed not be at a constant speed, and may be varied. For example, as theheating of the mixture becomes more uniform, the stirring rate may beincreased. The stirring may be at from about 10 revolutions per minute(rpm) to about 5,000 rpm, from about 20 rpm to about 2,000 rpm, or fromabout 50 rpm to about 1,000 rpm. A homogenizer (that is, a high sheardevice), may be utilized to form the phase inverted emulsion, but inexamples, the process of the present disclosure may take place withoutthe use of a homogenizer. Where utilized, a homogenizer may operate at arate of from about 3,000 rpm to about 10,000 rpm.

Following phase inversion, additional surfactant, water, and/or aqueousalkaline solution may optionally be added. For example, additional watermay be added to dilute the phase inverted emulsion, although this is notrequired. Following phase inversion, the phase inverted emulsion may becooled to room temperature (about 20° C. to about 25° C.), if necessary.

The processes of the present disclosure may include adding a surfactantto the resin, for example, before neutralization and/or during theaddition of the phase inversion agent, thereby enhancing formation ofthe phase inverted emulsion. Where utilized, one, two, or moresurfactants may be used. The surfactants may be selected from ionicsurfactants and nonionic surfactants. Anionic surfactants and cationicsurfactants are encompassed by the term “ionic surfactants.” Thesurfactant may, for example, be added as a solid or as a concentratedsolution with a concentration of from about 10% to about 100% (puresurfactant) by weight, or from about 15% to about 75% by weight. Thesurfactant may be utilized so that it is present in an amount of fromabout 0.01% to about 20% by weight of the resin, from about 0.1% toabout 10% by weight of the resin, or from about 1% to about 8% by weightof the resin.

Anionic surfactants which may be utilized include sulfates andsulfonates, sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate, sodium dodecylnaphthalene sulfate, dialkyl benzenealkylsulfates and sulfonates, acids such as abitic acid available fromAldrich, NEOGEN®, NEOGEN™ obtained from Daiichi Kogyo Seiyaku,combinations thereof, and the like. Other suitable anionic surfactantsinclude, in embodiments, DOWFAX™ 2A1, an alkyldiphenyloxide disulfonatefrom The Dow Chemical Company, and/or TAYCA POWER BN2060 from TaycaCorporation (Japan), which are branched sodium dodecyl benzenesulfonates. Combinations of these surfactants and any of the foregoinganionic surfactants may be utilized.

Examples of the cationic surfactants, which are usually positivelycharged, include, for example, alkylbenzyl dimethyl ammonium chloride,dialkyl benzenealkyl ammonium chloride, lauryl trimethyl ammoniumchloride, alkylbenzyl methyl ammonium chloride, alkyl benzyl dimethylammonium bromide, benzalkonium chloride, cetyl pyridinium bromide, C₁₂,C₁₅, C₁₇ trimethyl ammonium bromides, halide salts of quaternizedpolyoxyethylalkylamines, dodecylbenzyl triethyl ammonium chloride,MIRAPOL™ and ALKAQUAT™, available from Alkaril Chemical Company,SANIZOL™ (benzalkonium chloride), available from Kao Chemicals, and thelike, and mixtures thereof.

Examples of nonionic surfactants that may be utilized for the processesillustrated herein include, for example, polyacrylic acid, methalose,methyl cellulose, ethyl cellulose, propyl cellulose, hydroxy ethylcellulose, carboxy methyl cellulose, polyoxyethylene cetyl ether,polyoxyethylene lauryl ether, polyoxyethylene octyl ether,polyoxyethylene octylphenyl ether, polyoxyethylene oleyl ether,polyoxyethylene sorbitan monolaurate, polyoxyethylene stearyl ether,polyoxyethylene nonylphenyl ether, dialkylphenoxy poly(ethyleneoxy)ethanol, available from Rhone-Poulenc as IGEPAL CA-210™, IGEPAL CA-520™,IGEPAL CA-720™, IGEPAL CO-890™, IGEPAL CO-720™, IGEPAL CO-290™, IGEPALCA210™, ANTAROX 890™, and ANTAROX 897™. Other examples of suitablenonionic surfactants may include a block copolymer of polyethylene oxideand polypropylene oxide, including those commercially available asSYNPERONIC PE/F, in embodiments SYNPERONIC PE/F 108. Combinations ofthese surfactants and any of the foregoing nonionic surfactants may beutilized in embodiments.

In embodiments, the process of the present disclosure may include addingan anti-foam agent or defoamer to the phase inverted or resin mixtureaccording to the process and anti-foam agents or defoamers disclosed inU.S. Patent Application Publication No. 2010/0310983, incorporatedherein by reference in its entirety. A defoaming agent prevents foamingof the phase inverted mixture.

The processes of the present disclosure include adding a buffering agentto the phase inverted mixture. Buffering agents improve the stabilityand economics for making the polyester dispersions. Without beinglimited, it is theorized that the buffering agent adjusts the ionicstrength of the mixture, thereby increasing colloidal particle stabilityand increasing the stability of the electrostatic layer.

The buffering agent may be added to the phase inverted mixture, fromabout 0.01 to about 5.0 parts per hundred of the mixture based on theconcentration of the resin, for example, from about 0.05 to about 2.5parts per hundred of the mixture, or from about 0.1 to about 1 parts perhundred. Suitable buffering agents that may be utilized for theformulation of the present disclosure may include any salt, organiccompounds, any weak acid with its conjugate base, any weak base with itsconjugate acid, and mixtures thereof.

For example, suitable buffering agents which may be utilized includesalts of alkali metals, alkaline earth metals, for example sodiumchloride, or potassium chloride.

Suitable organic compounds include, for example, carbonates of alkalimetals, bicarbonates of alkali metals, sulfites of alkali metals,carbonates of alkaline earth metals, bicarbonates of alkaline earthmetals, sulfites of alkaline earth metals, for example, potassiumcarbonate, sodium bicarbonate, sodium sulfite and the like, and otherorganic compounds such as tris(hydroxymethyl)aminomethane (“TRIS”),Tricine, Bicine, Glycine, (4-(2-hydroxyethyl)-1-piperazineethanesulfonicacid (“HEPES”), trietholamine hydrochloride,3-(N-morpholino)propanesulfonic acid (“MOPS”).

In embodiments, a weak acid with its conjugate base, or a weak base withits conjugate acid, may be utilized as the buffering agent. A weak acidis an acid that partially ionizes in an aqueous solution and theconjugate base is the anion of the weak acid. A weak base is a base thatpartially ionizes in an aqueous solution and the conjugate acid is thecation of the weak base. Examples of weak acids include, for exampleacetic acid, oxalic acid, lactic acid, citrates and the like. Examplesof weak bases include ammonias, acetylacetone, methylamine, and thelike.

The above-mentioned buffering agent may be employed alone or in amixture of two or more thereof. The buffering agent may be added as anaqueous solution or as a solid. The buffering agent may be incrementallyadded to the resin mixture.

After addition of a buffering agent to the phase inverted mixture, theorganic solvent of the resin mixture is substantially removed, forexample, by distillation, such as vacuum distillation. Vacuumdistillation is a method of distillation whereby the pressure above theliquid mixture to be distilled is reduced to less than its vaporpressure causing evaporation of the most volatile liquid. Thisdistillation method works on the principle that boiling occurs when thevapor pressure of a liquid exceeds the ambient pressure. Vacuumdistillation may be used with or without heating the phase invertedmixture.

After distillation, some residual solvent may remain in the final latex.The residual solvent in the final latex ideally contains less than 600ppm, such as less than about 500 ppm, less than about 300 ppm, or lessthan 100 ppm of solvent.

This process offers several advantages over current solvent-basedprocesses for the formation of emulsions both at the laboratory andindustrial scale. The process of the adding a buffering agent mayincrease the stability during the transportation and storage bypreventing sedimentation and prevent the latex mixture from gellinginside the reactor. In addition, the process of the present disclosurefor the production of polyester latex emulsions using PIE permits highthroughput experimental screening, high throughput production rates,eliminates or minimizes wasted product, greatly reduces time to marketfor the latex production, and produces latexes with more efficientsolvent stripping.

The emulsified resin particles in the aqueous medium may have asubmicron size, for example of about 1 μm or less, about 500 nm or less,for example, from about 10 nm to about 500 nm, from about 50 nm to about400 nm, from about 100 nm to about 300 nm, or about 200 nm. Adjustmentsin particle size can be made by modifying the ratio of water to resinflow rates, the neutralization ratio, solvent concentration, and solventcomposition. Distillation with stirring of the organic solvent may beperformed to provide the polyester resin emulsion particles with anaverage diameter size of, for example, from about 50 nm to about 250 nm,or from about 120 to about 180 nm.

The polyester emulsions may also have a high product yield by reducingreactor fouling and increasing reactor loading. Accordingly, a cleanpolyester dispersion with less residual solvents is produced. Inaddition, the final latex produced by the process may be used to formtoner particles in any emulsion-aggregation process known in the art.

EXAMPLES Example 1 Preparation of Crystalline Polyester Latex withBuffer

A 2 L-scale phase inversion emulsification (PIE) process was developedfor screening of buffer efficiency. About 10 wt % of a highmolecular-weight polyester resin, crystallinepoly(dodecandioicacid-co-nonanediol), about 6.0 wt % of methyl ethylketone (MEK) and about 1 wt % of 2-propanol (IPA) were added to a glassreaction vessel, heated up to about 75° C., and allowed to dissolve. Theresin liquid was then cooled to 60° C. An ammonia solution with aneutralization ratio of 114% was added to the resin liquid over a periodfrom about 5 minutes to about 10 minutes under sufficient mixing. Themixture was allowed to mix for an additional 10 to 30 minutes. A phaseinversion agent, about 30 wt % of resin weight of warm water, at about60° C., was added to the resin mixture at a rate of about 2.2% of resinweight per minute. Latex was made when the addition of the water inducedphase inversion from water-in-oil to oil-in-water, resulting in auniform dispersion of polyester latex particles in water.

Before vacuum distillation, a solution of about 0.1 parts per hundred toabout 1 part per hundred, based on the concentration of resin, of sodiumbicarbonate (NaHCO₃) was added as a buffer to the reactor at a rate ofabout 2.2% of resin weight per minute over about 5 minutes. The reactorwas then heated to about 60° C. Once the reactor reached a temperatureof about 55° C., a vacuum was applied to the reactor until a vacuum ofabout 65 mm of Hg was achieved after about 45 minutes.

During distillation, defoamer Tego Foamex 830™ was incrementally added,up to about 700 parts per million (ppm), through a charge line on top ofthe reactor. Samples were taken during distillation, and the residualMEK and IPA levels were measured by gas chromatography. The final latexhad a residual MEK of less than about 20 ppm and residual IPA of lessthan about 80 ppm. The latex was stable, with a particle size a particlesize of about 150 nm and a solids content of about 35 weight %.

The final latex was tested for % of sedimentation and stability againstshear using a kitchen blender (Oster 12 speed blender) at the lowestspeed setting. The test results are summarized in Table 1.

Comparative Example 1 Preparation of Crystalline Polyester Latex withoutBuffer

A polyester latex was prepared using the same formulation and processconditions described in Example 1, except that no buffer was addedbefore distillation. Distillation was stopped early, when the residualamount of MEK and IPA was about 800 ppm. The final latex was tested for% of sedimentation and stability against shear using a kitchen blender(Oster 12 speed blender) at the lowest speed setting. The test resultsare summarized in Table 1.

Comparative Example 2 Preparation of Crystalline Polyester Latex withoutBuffer

A polyester latex was prepared using the same formulation and processconditions described in Example 1, except that no buffer was addedbefore distillation. Distillation was attempted to remove additionalsolvent from Comparative Example 1, but it was found that the latexgelled inside the reactor when the residual MEK and IPA was about 600ppm.

TABLE 1 Final Latex Properties Time To Buffer Residual Residual ParticleSize gelation NaHCO₃ Final Latex MEK IPA Size Distribution under shear %Sample ID (pph) Resulted (ppm) (ppm) (nm) (mv/mn) (seconds)Sedimentation Latex 0.5 Yes 20 80 150 1.61 90 0.15 Example 1 Latex 0 Yes45 750 153 1.72 60 0.48 Comparative Example 1 Latex 0 No, latex N/AComparative gelled during Example 2 distillation

The results in Table 1 indicate that the addition of buffer to the phaseinverted mixture before distillation improves stability of the latex andprevents gelling of the latex. For example, without the addition ofbuffer, Comparative Example 2 demonstrates that the latex gels in thereactor when the residual solvents drop near 600 ppm, thus yielding nofinal latex.

Furthermore, Example 1 and Comparative Example 1 indicate that thebuffer does not affect the particle size and size distribution of thefinal latex, but does improve stability of the final latex. The latexparticle size was characterized by utilizing a Honeywell MICROTRAC® UPA150 light scattering instrument. The size distribution is the ratio ofweight average size (MV) to the number average size (MN). For example,the % of latex sedimentation decreased and time to gelation under shearincreased in Example 1 (with buffer) when compared to a similar samplewith no buffer (Comparative Example 1).

Example 2 Emulsion Aggregation (EA) Particle Formation and TonerProperties

A polyester dispersion was doped with about 0.5 pph NaHCO3 based oncrystalline polyester resin and converted to particles in a 20-gallonreactor using an EA particle process. The doped polyester dispersion ofExample 1 comprised the same characteristics as that of a normalpolyester dispersion without buffer, as shown below in Table 2.Specifically, toner particles having no buffer and toner particleshaving buffer possessed very similar properties, including NumberAverage Geometric Size Distribution (GSDn), Volume Average GeometricSize Distribution (GSDv), and Circularity (Cir.).

TABLE 2 Comparison of Black Parent Particle/Toner Properties CPEParticle Particle Toner Toner Toner Residual T½ by latex with Size TriboTribo Tribo Tribo ions Shimadzu Samples buffer (μm) GSDv GSDn Cir. (Bzone) (A zone) (B zone) (J zone) (ppm) (° C.) Toner Yes 5.64 1.20 1.220.972 66 28.6 48.6 56.7 1150 96.5 Example 1 Toner No 5.61 1.20 1.220.971 65 27.0 49.0 57.0 1165 96.4 Comparative Example 1

Particles made from doped polyester dispersion were further converted totoner particles with additives and evaluated. The results summarized inTable 2 indicate that a toner produced in accordance with the presentdisclosure contains similar properties to a toner produced using a latexwithout the addition of buffer. Toner Example 1 was produced from LatexExample 1 of Table 1, and Toner Comparative Example 1 was prepared fromLatex Comparative Example 1. See Table 1 and 2.

The characteristics of the toner particles may be determined by anysuitable technique and apparatus. GSDv and GSDn were measured by meansof a measuring instrument such as a Beckman Coulter Multisizer 3,operated in accordance with the manufacturer's instructions.Representative sampling occurred as follows: a small amount of tonersample, about 1 gram, was obtained and filtered through a 25 micrometerscreen, then put in isotonic solution to obtain a concentration of about10%, with the sample then run in a Beckman Coulter Multisizer 3.Circularity was measured with, for example, a Sysmex FPIA 2100 analyzer.

Toners produced in accordance with the present disclosure possessedsimilar tribo characteristics when exposed to extreme relative humidity(RH) conditions. The low-humidity zone (J-zone) is about 70° F./10% RH,while the high humidity zone (A-zone) is about 80° F./80% RH. Inaddition, the tribo of toners made from polyester latexes derived fromthe processes of the present disclosure have similar characteristics inambient conditions (B-zone) of about 70° C./50% RH.

The residual ions of the toner particles are measured by instrumentalelemental analysis with Inductively Coupled Plasma (ICP) OpticalEmission Spectroscopy. 0.25 grams of each sample were placed intoseparate platinum crucibles. 0.6 grams of 50/50 LithiumTetraborate/Lithium Metaborate flux is added to the samples. The samplesare heated to flux temperature of 300° C. for 1 hr, 600° C. for 4 hrs,or 950° C. for 40 min. 15 ml of 50% HCl is added to the samples and thesamples are heated on a hot plate until dissolved. The samples aretransferred to 100 mL plastic volumetrics and 0.5 mL of concentrated HFis added to the samples. 7.5 mL of 4% H₃BO₃ solution is added toneutralize any excess HF and let stand for at least one hour. Afterstanding, 1 mL of 5% Triton X-100 is added as a wetting agent andbrought to mark using DI water. Samples are analyzed on the TJA IRISICP.

The softening point and melt flow behavior of toners is determined usinga Shimadzu CFT500. Data is reported in terms of softening point (Ts);the point at which the material begins to flow (Tfb) and the point atwhich one half of the material has been extruded, T^(1/2). Approximately1.6 grams of the samples is separately pressed into pellets at 5000 lbspressure and analyzed using a Shimadzu CFT-500D capillary flow testerwith 1.0 mm×1.0 mm die and 30 kg of weight. The sample is placed in theinstrument at 40° C. and heated at about 3° C./minute to 140° C.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

What is claimed is:
 1. A method comprising: mixing at least onepolyester resin with at least one solvent to form a resin mixture;adding water to cause phase inversion and form a polyester latex; addingat least one buffering agent to the phase inverted mixture to stabilizethe phase inverted mixture; and subsequent to the buffering agentaddition, substantially removing the at least one solvent from the phaseinverted mixture, wherein before the phase inversion, a neutralizingagent is added to the resin mixture.
 2. The method according to claim 1,wherein the at least one solvent is selected from the group consistingof ketones of the formula (C_(n)H_(2n+2))CO, polyols of the formulaC_(n)H_(2n+1)OH, acetates of the formula C_(n)H_(2n+2)OCOCH₃, ormixtures thereof, wherein n is greater than or equal to
 1. 3. The methodaccording to claim 1, wherein the at least one polyester resin is acrystalline polyester resin, or a mixture of a crystalline polyesterresin and an amorphous polyester resin, and wherein the solvent to resinweight ratio in the resin mixture is from about 0.3 to about
 3. 4. Themethod according to claim 1, wherein the neutralizing agent is added asan aqueous solution, the water of the aqueous solution being the watercausing the phase inversion.
 5. The method according to claim 1, whereinthe water is added as deionized water, or as an aqueous solutioncontaining water, and wherein the water to resin weight ratio followingaddition is from about 5 to about
 50. 6. The method according to claim1, wherein the at least one buffering agent is selected from the groupconsisting of a buffer or a mixture of buffers, and wherein aconcentration of the buffer is from about 0.01 to about 5 parts perhundred of the mixture.
 7. The method according to 6, wherein the bufferis selected from the group consisting of at least one salt, at least onesolution of at least one weak acid and at least one conjugate base, atleast one solution of at least one weak base and at least one conjugateacid, or mixtures thereof.
 8. The method according to claim 1, wherein asurfactant is added before or after phase inversion, and wherein adefoaming agents added after phase inversion.
 9. A method comprising:mixing at least one polyester resin with at least one solvent to form amixture; phase inverting the mixture by adding water; buffering thephase inverted mixture; preventing foaming of the buffered phaseinverted mixture by using a defoaming agent; and subsequent to thebuffering, substantially removing the at least one solvent from thephase inverted mixture.
 10. The method according to claim 9, wherein thebuffering of the phase inverted mixture occurs from the addition of atleast one buffer.
 11. The method according to claim 10, wherein the atleast one buffer is mixed with the phase inverted mixture beforeremoving the at least one solvent from the phase inverted mixture. 12.The method according to claim 9, wherein, before phase inversion occurs,neutralizing the mixture with a neutralization agent.
 13. The methodaccording to claim 9, wherein the substantially removing the at leastone solvent occurs by distillation to less than 600 ppm of the solvent.